1. Field of the Invention
This invention relates to an improved system including a probe, electronic circuit, and display panel for measuring and displaying the level of a liquid in a container.
2. Description of Related Art Including Information Disclosed under Secs. 1.97-1.99
Motor vehicles have long been provided with dip sticks for measuring the level of the oil in the engine oil pan and in the automatic transmission housing. Indicators, such as lights on the instrument panel have also been provided to warn the operator of low liquid levels. Measuring fluid levels with a dip stick, being a time consuming task, is often not regularly performed by the operator. While so called full service fuel stations do check fluid levels, with the hope of selling the needed fluid, self-service station do not offer that service. The result is that many operators do not regularly check fluid levels.
Attempts made in the past to provide means for measuring the levels of the several liquids used in motor vehicles are represented by the following United States Patents:
______________________________________ U.S. Pat. No. INVENTOR ISSUE DATE ______________________________________ 3,132,331 Boddy 5/5/64 3,626,367 Howard et al 12/7/71 3,728,704 Moore 4/17/73 4,110,740 Akita et al 8/29/78 4,322,713 Duck et al 3/30/82 4,503,419 Kidd et al 3/5/85 4,506,258 Charboneau et al 3/19/85 4,751,845 Peterson et al 6/21/88 4,910,495 Sullivan 3/20/90 4,912,646 Cerruti 3/27/90 4,952,914 Mueller 8/28/90 ______________________________________
One type of system used to measure the level of fluids utilizes a float, which is buoyant in the fluid being measured, to provide an input to an electronic circuit. The patents to Moore, Sullivan and Cerruti reveal systems of this type. Another approach is to use the conductivity of the fluid to complete an electrical circuit. Devices utilizing this approach are shown in the Akita et al, Duck et al, Peterson et al and Mueller patents. Still another approach is represented by the Boddy patent which involves the measurement of fluid pressure. The Duck et al patent sets forth an extensive list of patents directed to fluid level measurement systems. The Howard et al and Kidd et al patents do not reveal the type of sensors used to measure fluid levels, but do reveal electronic circuits for fluid level measuring systems.
The Charboneau et al patent reveals a system for actuating a warning device for indicating a low level of a liquid in a receptacle, such as the oil pan of the engine. The sensing element as disclosed in the Charboneau et al patent includes several convolutions of a positive temperature coefficient wire which are submerged in the fluid unless the fluid drops below a predetermined low level. The circuit set forth in the Charboneau et al patent activates a warning device when the fluid reaches the predetermined low fluid level. The sensor described in the Charboneau et al patent is of a rather complex construction, and the electronic circuit used therewith does not reveal a method for providing an indication of the fluid level, other than that it is below a preselected lower level. Thus, the provision of a sensor employing a positive temperature coefficient material of simpler construction and of a circuit which will provide on demand an indication of the current fluid level is desirable.